Smartmatrix 4.0 feedback

Howdy,

So, I just got the chance to try a couple of smartmatrix 4 boards I bought from adafruit.
Some feedback:

  1. really cool that you can just plug it in the panel, plug the teensy on the other side, and you’re done. Very cool design/idea

  2. honestly it feels weird and unnecessary to have APA102 support
    a) arduinos can do WS2812B timing well enough that virtually no one buys the more expensive APA102s when you have FastLED support on your microcontroller
    b) I’m not very likely to buy a smartmatrix to control an APA102 when a simple level shifter would do the job (or maybe it just works with 3.3V like many WS2812B chips)
    c) if I’m driving LED panels, why would I also want to run APA102 at the same time, feels weird.

  3. ok, I can use the APA102 connector to connect power from the board to the panel. Actually I was going to power the panel from my laptop without another power supply because my laptop can output 2A over USB. Well, except that the copper trace on the board is too thin and doesn’t pass the 2A.
    I had to work around it by soldering my own wires back to the teensy to bypass the copper trace and now it works. It passes enough power that if I make things too bright, it’ll hit the 2A current limit on my laptop.

Still, something worth improving for v5 I guess :slight_smile:
But overall I really like the board, thanks for making it, and can’t wait for an ESP32 version (except for the sad part that ESP32 chips all seem to have different pinout, which really sucks for making a board like this :-/ )

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I ended up soldering an angled connector on one, and just soldering a JST cable on the other one. May be nice to offer a header for VCC + Gnd side by side for soldering an angled JST connector? (I didn’t plug into the mirror pins of the teensy because I didn’t want to solder there and keep those holes pristine for push through wires, as well as as didn’t want my power connector to point up and stick out too much).


  1. really cool that you can just plug it in the panel, plug the teensy on the other side, and you’re done. Very cool design/idea

Thanks, but I can’t take credit for that, I got the idea from the Particle Internet Button

  1. honestly it feels weird and unnecessary to have APA102 support

True, it’s a bit weird to have the APA102 connector on there when I’m not doing much with it, but I have plans for it in the future. I like the 2-wire LEDs a lot better than WS2812s because of the Global Brightness Control bits which you can use to get a lot higher color depth out of these LEDs. See the demo and some details I posted here describing this and the video comparing FastLED dithering with APA102 GBC:

c) if I’m driving LED panels, why would I also want to run APA102 at the same time, feels weird.

Most obvious example is driving Ambilight-style background lighting behind your HUB75 panels. Another is driving the sleeves of your shirt synced up to the panel in front.

Well, except that the copper trace on the board is too thin and doesn’t pass the 2A

This is on purpose as the Teensy 3.2 has a fuse between the V+ input on the USB connector and the VIN pin. Teensy 3.6 doesn’t but I think for most people trying to power the Teensy and panel from USB is a bad idea, and I’d rather not support it. https://www.pjrc.com/teensy/schematic.html

I’m running out of time and maybe I’m missing something in your picture, but I don’t understand why you need to feed power to the shield in more than one place. The shield isn’t designed to run power for your panel through it. You can connect your power source to your panel, and then connect either your power source to the shield, or connect the power at the panel to the shield.

Thanks for adding to the community by responding to some posts on your first visit here.

  • Louis
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Just in case you didn’t see it already: SmartMatrix Library ESP32 Port

I agree there are too many form factors for ESP32 boards. I probably won’t be releasing a shield for ESP32, at least not anytime soon, but everything I’ve done on the project is open source and at least partially working

Yes, I saw the ESP32 port and will definitely look at it, but I figured I’d try with your shield since it was so convenient to buy and plug in.
On the power delivery, yes I of course agree that one should not power from USB in production, it’s just useful to do during development.
For the fuse, I looked at https://www.pjrc.com/teensy/schematic.html and it seems to be after Vin, so if I connect to Vin, it gets power from USB before the fuse. I already passed 2A with my wire bypass (limit of my laptop USB) and it worked without issues.
Am I missing something?
The only (expected) downside is that if I power too much and hit the 2A limit, I lose USB power and the teensy resets. I can live with it for hacking on a couch with my laptop though :slight_smile:

I already read in another post you wrote that you’re not planning on doing a V5 shield, so you can ignore my suggestions for a new version, but to answer your question, I had one of my 2 shields with power connected in 2 places just for testing, only my newly soldered JST plug that goes directly to GND and Vin, is really passing the power.
Once in production, power would go to the panel and feed the teensy as opposed to coming from USB to power the teensy and the panel, as you point out. It’s just a pain to have to separately power the panel from a wall 5V source when I’m working on my laptop.

As to how I could use APA102 to power my shirt pixel trips, touché, I kind of thought of that too :slight_smile: except that I really have no reason not to stick with the WS2813B strips (redundant data) that I already have and that work fine.
That said, point taken that APA102 gives you better control control with brightness.

Thanks and kudos for all your work with this lib and the shield and this community.
While a few dollars here and there may not change your life much, have you considered a donate link?

Scroll down to the Teensy 3.2 schematic, the fuse is between the USB connector and VIN.

I already read in another post you wrote that you’re not planning on doing a V5 shield

I’m not ruling it out, and I am collecting a list of improvements for the future, thanks for the feedback.

I really have no reason not to stick with the WS2813B strips (redundant data) that I already have and that work fine.

With the tip of a knife or thin screwdriver you could probably push the JST-SM crimps out of the 4-pin connector housing and push them into a 3-pin housing, or just use three conductors from the included mating JST-SM cable. Lots of options.

I’ve had a couple people ask me to start a Patreon, but I haven’t done the research. Maybe I will someday, thanks!

@Louis you are correct, I was looking at the wrong schematic.
Teensy 3.5/3.6 passes USB power through, 3.2 does not. And yet, I was able to get 2A to my panel through USB and get proper display though a teensy 3.2. The polyfuse on 3.2 is not labelled though, not sure what value it is.
Either way, I’ve switched to 3.6 for good now, so I can not worry about this and pass through 2A from my laptop directly to the panels through your board after I added my bypass wires.
That being said, if you do a V5, I don’t think there is a point limiting amps on the board as long as teensy 3.1 and 3.0 also have polyfuses and not regular burnable fuses.

oh yeah, for patreon, sure you can look at that when you get time, but I find a simple paypal link and google wallet if it works in your country, and/or an amazon donation shopping list are simple way to get donations too and much quicker to setup :slight_smile:

From memory, I think the fuse was set to limit current to 500mA (or rather to guarantee not to trip until somewhere above 500mA)

Not pretty (no button/image), but this should work (thanks for the idea!):

Donate to Pixelmatix

No button needed :slight_smile:
Now you can add it on https://github.com/pixelmatix/SmartMatrix , http://docs.pixelmatix.com/SmartMatrix/, and other places that make sense :slight_smile:

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